In the process for producing an aromatic polycarbonate resin according to an interfacial polymerization method, when gaseous phosgene was injected into a mixture of an alkali aqueous solution of bisphenol and methylene chloride with stirring, a low molecular weight polycarbonate with chloroformate group on its ends was initially produced in a solvent. However a large amount of cooling water was necessary to control the reaction temperature because the reaction of an alkali salt of bisphenol and phosgene was rapid and an exothermic reaction. Further, it was required to maintain the reaction temperature to a low temperature of around 20° C. from the viewpoints of decomposition of phosgene and color of an aromatic polycarbonate resin thus obtained.
Japanese Patent Publication No.46-21460 discloses a process for producing continuously a polycarbonate oligomer which comprises introducing an alkali aqueous solution of bisphenol and an organic solvent for polycarbonate oligomer into a tubular reactor to form a mixed phase flow and performing a parallel flow reaction with phosgene and temporarily removing reaction heat generated during the reaction by vaporization latent heat of said organic solvent. However, in this process, the reaction is a parallel flow reaction in a tubular reactor and no stirring is performed. Further, the tubular reactor is a double tube in which cooling water is passed through a jacket portion. The generated reaction heat is temporarily removed by vaporization latent heat of the organic solvent, but a majority of the reaction heat is removed by the cooling water of the jacket portion. Further, in this process, gas-liquid separation of the reaction product is necessary, so that both operation and apparatus become complicated.
Thus, Japanese Patent Kokai (Laid-open) No.58-108225 suggests a process for producing a polycarbonate oligomer which comprises reacting an alkali aqueous solution of a dioxy compound and phosgene in the presence of an organic solvent, wherein a cooling jacket is provided with a reaction tube to maintain the temperature range of the reaction to 2 to 20° C. In order to perform efficiently cooling, it is necessary to make the tube diameter small. However, in such case, there occurs a dilemma that it becomes difficult to perform smoothly the reaction of mist droplet and gas in the reaction tube. Further, also in this process, a cooling medium of 0° C. or below to maintain to a low temperature was required.
On the other hand, Japanese Patent Publication No.54-40280 suggests a process for removing reaction heat to be generated during reaction which comprises contacting initial reaction product with a large amount of reaction products maintained to a constant temperature. However, in this process, it was not only difficult to control initial stage of phosgenating reaction, but it was difficult to avoid decomposition of both phosgene and chloroformate.
Further, Japanese Patent Kokai (Laid-open) No.55-52321 suggests a process for absorbing effectively reaction heat which comprises cooling an alkali aqueous solution of bisphenol to 0° C. or below and reacting the cooled aqueous solution and phosgene. However, in this process, although the reaction temperature could be made low, the contact of methylene chloride to be often used as an organic solvent with the aqueous solution in such a low temperature caused formation of a hydrate. Thus, the reaction system became a sherbet state, so that various inconveniences occurred and it was practicality improper.
As a process for removing such reaction heat, Japanese Patent Kokai (Laid-open) No. 47-14297 suggests a process for producing continuously a high molecular linear polycarbonate which comprising again feeding cooled high molecular weight reaction mixture. In this process, gas-liquid separation of reaction product was necessary because phosgene diluted with another inert gas was charged. Further there was a problem that decomposition of both phosgene and chloroformate became even large because amine was present and the system readily became an emulsion state.
Hitherto, regarding removal of reaction heat to be generated during phosgenating reaction of an aromatic polycarbonate resin (polycarbonate oligomer production reaction), the reaction was performed at a temperature of around 20° C. from the problems of decomposition of phosgene, blowing-out of phosgene and vaporization of reaction solvent. Therefore, a process for passing a cooling medium through a jacket or an inner coil to remove reaction heat and a process for performing external circulation of a reaction liquid to cool through a heat exchanger have been applied. However, in such processes, duty of electrical energy was enormous because a cooling medium of 0° C. or below was necessary and thus a refrigerator for production of a cooling medium was required.